1. Field of the Invention
The present invention relates to a method for forming a deep trench. In particular, the present invention relates to a method for forming a deep trench by using a liner in combination with a selective etching procedure.
2. Description of the Prior Art
In a dynamic random access memory (DRAM), conventionally two types of capacitors are used, and one of them is called a deep trench capacitor. In the process of forming the deep trench capacitor, usually a shallow trench is first formed by dry etching and further the depth is accomplished under the protection of a layer of SiO2. Finally, the surface area is enlarged by wet etching under the protection of a layer of aluminum oxide. Such procedure requires two kinds of etching mask for protection.
Therefore, a novel process is needed for forming the deep trench capacitor with sufficient depth and surface area.